1. Field of the Invention
The present invention relates generally to the deposition of diamond films on substrates, and more specifically to vapor deposition of diamond upon a substrate.
2. Description of the Prior Art
Metallic, inorganic, and organic coatings are applied to metals, alloys and other materials to prevent chemical corrosion, oxidation, or other forms of environmental degradation. Nevertheless, these coatings are not completely inert to the environment and eventually fail chemically and/or mechanically, thereby exposing the substrate.
Diamond is inert in a variety of environments including inorganic acids, bases, and organic solvents. Solutions such as hot aqua regia (a mixture of 2/3 hydrochloric acid and 5/8 nitric acid), hot aqua-fortis (2/3 sulfuric acid and 5/8 nitric acid), and hot caustic solutions (potassium hydroxide) have been used to clean diamond with no apparent damage to the diamond. Also, diamond is inert in chloride environments. For example, in an 8% NH.sub.4 Cl solution, diamond was not degraded at potentials below 80 volts.
Diamond films have been produced at low pressures and on larger areas. Diamond films have high thermal conductivity, are electrically insulating, have a very good abrasion resistance, and desirable optical properties. These properties and the fact that diamond is inert in a variety of environments suggest that diamond films could be used as protective coatings.
Diamond films and microcrystals have been previously produced by Filament Assisted Chemical Vapor Deposition (FACVD). That technique consists of passing a mixture of hydrogen and a hydrocarbon gas, such as methane, over a filament heated to about 2000.degree. C. The diamond is deposited on a substrate which is heated to about 800.degree.-1000.degree. C., and positioned near the filament. This work is done in a vacuum chamber at typical pressures of 20-100 torr. The material from which the diamond is actually produced is a mixture of hydrogen and methane. The proportion of these two gases is generally 100:1. Many researchers have noted that while diamond may be grown on a variety of materials (Mo, Ni, Cu, Si, SiC, WC, etc.), the nucleation density is enhanced when the surface of the material is scratched with diamond grit. Also diamond seems to nucleate strongly on areas of hydrocarbon contamination which are not removed during substrate cleaning.